This invention relates to a magnetic disk device, a magnetic head slider and a method of producing the same. More specifically, the invention relates to a magnetic head slider in which a thin-film head portion is formed on a silicon substrate portion, and a magnetic disk device using the magnetic head slider. The expression of recording/reproduction in the following description includes the recording only, reproduction only and both the recording and the reproduction.
In a magnetic disk device, a magnetic head slider mounting a recording/reproducing element floats on the magnetic disk due to the pneumatic wedge film effect to record/reproduce the magnetic data recorded in the magnetic disk. To realize a high recording density of the magnetic disk device and an accompanying large capacity of the device or a decrease in the size, it is essential to decrease the distance (slider's flying height) between the magnetic head slider and the magnetic disk and to increase the linear recording density. In recent years, the flying height has been decreased to be about 10 nm or not larger than 10 nm.
A magnetic head slider generally employed in the conventional magnetic disk devices is constituted by a slider substrate portion and constituting formed on the slider substrate and an air-bearing surface along with the slider substrate.
The above conventional and generally employed magnetic head sliders are produced in a manner of laminating a metal film, a ceramic insulating film and a resin film etc. relying on a thin-film process on a wafer of a mixed sintered body of alumina and titanium carbide (often noted as AlTiC), forming recording/reproducing elements thereby to form a plurality of magnetic head slider portions and, finally cutting the individual magnetic head sliders from the wafer by machining without, however, being able to avoid low productivity.
Therefore, there has been devised a magnetic head slider using silicon as a material of the slider substrate portion instead of using AlTiC as disclosed in a non-patent document 1 (IEEE Transactions on Magnetics, Vol. 40, No. 1, pp. 332-336, Flying-height adjustment technologies of magnetic head sliders). The object of using silicon as a material of the slider substrate portion is to decrease the cost by forming the outer shape of the slider by cutting the slider substrate relying upon etching instead of upon machining.
In the conventional generally employed magnetic head slider comprising the slider substrate portion made of AlTiC and the thin-film head portion having a metal film and a ceramic insulating film, however, it was learned that if the material forming the slider substrate portion is changed from AlTiC into silicon, then, the thin-film head portion is thermally dented or protruded due to a change in the environmental temperature and the reliability decreases though it brings about an advantage such as a decreased machining cost. The thermal dent or protrusion caused by a change in the environmental temperature stems from that the coefficient of linear expansion of the metal film greatly differs relative to the slider substrate portion or the ceramic insulating film, and a slider-floating plane (also called air-bearing surface) that is supposed to have been smoothly finished becomes finely dented or protruded when the temperature is low or high.
The coefficient of linear expansion of the metal film is generally greater than that of the slider substrate portion or of the ceramic insulating film and, hence, the slider-floating plane that is supposed to have been smoothly finished tends to become protruded when the temperature is high. Therefore, a distance (slider floating amount) between the magnetic head slider and the magnetic disk becomes smaller than a designed value, and the magnetic head slider becomes probable to come in contact with the magnetic disk. If the magnetic head slider and the magnetic disk come in contact with each other, it becomes impossible to record/reproduce the magnetic data being affected by vibration due to friction, and the recording/reproducing element tends to be worn out and damaged. In order to avoid the contact even at high temperatures, the floating amount must be designed to be sufficiently large, making it, however, difficult to improve the recording/reproducing performance. At low temperatures, on the other hand, the metal film forming the recording/reproducing element tends to be dented from the floating plane, whereby the distance between the recording/reproducing element and the magnetic disk becomes greater than the designed value to deteriorate the recording/reproducing performance.
The thermal dent or protuberance due to a change in the environmental temperature had been taking place even in the conventional generally employed magnetic head slider constituted by a slider substrate portion made of AlTiC and a ceramic insulating film formed chiefly by alumina. However, if the material forming the slider substrate portion is changed from AlTiC into silicon and if the material forming the ceramic insulating film is changed from alumina into silicon-based ceramics such as silica, silicon carbide or silicon nitride, then, the thermal dent or protuberance further increases due to a change in the environmental temperature. The reason will be described below with reference to Table 1. Table 1 shows the materials of the chief constituent elements and coefficients of linear expansion thereof of a conventional generally employed magnetic head slider and of a magnetic head slider using a silicon substrate of Comparative Example.
TABLE 1Conventional generalMag. head slider usingmag. head sliderSi substrateChief metal film materialferronickelferronickel(coefficient of linear(13 ppm/K)(13 ppm/K)expansion)Substrate materialAlTiCsilicon(coefficient of linear(about 7 ppm/K)(about 3 ppm/K)expansion)Chief ceramic insulatingaluminaSilicon-based ceramicsfilm material(about 7 ppm/K)(about 3 ppm/K)(coefficient of linearexpansion)Difference in the6 ppm/K10 ppm/Kcoefficient of linearexpansion between metalfilm/substrate or betweenmetal film/insulating film
As shown in Table 1, a metal film of an alloy of chiefly nickel and iron used for the recording/reproducing element has a coefficient of linear expansion of about 13 ppm/K (13/1,000,000 per a degree of temperature), AlTiC and alumina have a coefficient of linear expansion of about 7 ppm/K, and silicon and silicon-type ceramics have a coefficient of linear expansion of about 3 ppm/K. Thermal dent or protuberance at high temperatures or at low temperatures occurs due to a difference in the coefficient. In the conventional generally used magnetic head slider, a difference in the coefficient is about 6 ppm/K while in the magnetic head slider using the silicon substrate of Comparative Example, a difference in the coefficient is about 10 ppm/K which is about five-thirds as great. That is, though the magnetic head slider using the silicon substrate has several advantages, it also is accompanied by a problem in that the thermal dent or protuberance due to a change in the environmental temperature becomes greater than that of the conventional general magnetic head slider.
It is a feature of the present invention to provide a magnetic disk device which helps increase the productivity of the magnetic head sliders while lowering the cost, maintains reliability by compensating for the thermal dent or protuberance caused by a change in the environmental temperature, and makes it possible to increase the recording density by decreasing the floating amount of the slider, to increase the capacity of the device or to decrease the size thereof, a magnetic head slider and a method of producing the same.